How do you know? Has there been a poll I missed?
I am willing to see the benefits if there are any.
I see the idea as: if there is already (semantically) similar data somewhere in a field, please spare me the effort of having to retype it but offer it in a dropdown list.
Is that about the gist of it?
If so, then please expand that idea not only to your immediate needs but also to the other fields that I already mentioned:
For EPs the TITLE is very often the ALBUM - the title would then be a fairly good suggestion for the album and get into the album dropdown list.
For many tracks, the ARTIST is also the COMPOSER - the artist name would then also be a good suggestion for COMPOSER and get into the the composer dropdown list.
Sometimes the first ALBUM of an ARTIST has the artist's name - the artist name would then also be a good suggestion for ALBUM.
So the dropdown lists would become fairly congested I assume, as I see the data from artist, albumartist, title, album, composer all in the same list - just to avoid typing. And MP3tag would not know which data is more important for you.
And this long list is of benefit?
A limitation to just ARTIST and ALBUMARTIST would leave out all those who follow other approaches and see similarities as described in the above list.
The ususal turn in the controverse discussions about featues is: well, then make it an option, so that those who do not want it, don't have to bother.
But this option is already there: use an action that suits your needs. This will copy data from any field into any other, even with some kind of intelligence, if you use filters or $IF().
The only difference between the original suggestion and the already existing functions is that the approach is a little different: you have to do the programming instead of the author.
The outcome is the same in the end: you have copied data from ARTIST into ALBUMARTIST.
I am in no position to grant or refuse any feature requests.
On the other hand I like to offer options that a certain problem can be overcome (in the meantime until the verdict is passed).
This offer remains the same: create yourself an action that copies ARTIST into ALBUMARTIST.